Photoelectric Conversion Device and Method for Producing Photoelectric Conversion Device

ABSTRACT

A photoelectric conversion device according to the present invention has a plurality of photoreceiving portions provided in a substrate, an interlayer film overlying the photoreceiving portion, a large refraction index region which is provided so as to correspond to the photoreceiving portion and has a higher refractive index than the interlayer film, and a layer which is provided in between the photoreceiving portion and the large refraction index region, and has a lower etching rate than the interlayer film, wherein the layer of the lower etching rate is formed so as to cover at least the whole surface of the photoreceiving portion. In addition, the layer of the lower etching rate has a refractive index in between the refractive indices of the large refraction index region and the substrate. Such a configuration can provide the photoelectric conversion device which inhibits the lowering of the sensitivity and the variation of the sensitivity among picture elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion device usedin a digital camera or the like, which forms an image by convertingincident light to an electric charge.

2. Related Background Art

For an image input device like a digital camera, a video camera and animage reader, a photoelectric conversion device is used such as a CCD(Charge Coupled Device) image sensor, or a non-CCD image sensor like abipolar transistor image sensor, a field-effect transistor image sensor,a CMOS (Complementary Metal Oxide Semiconductor) image sensor and thelike. The photoelectric conversion device converts optical imageinformation to an electric signal, and the image input device processesthese various converted electric signals to display them on a displayfor indication or record them in a storage medium.

In order to acquire high performance, a photoelectric conversion deviceis desired to increase the number of photoelectric conversion elementsto be arranged thereon, by reducing the area (picture element area) of aphotoreceiving region of the photoelectric conversion element, and toreduce its chip size. Such a photoelectric conversion device has amicrolens arranged on a photo diode. The structure is designed so thatthe focal position is set in the vicinity of a photoreceiving portion ofthe photo diode.

However, as picture elements are compacted and a tip is downsized, asmaller proportion of a light condensed by a microlens enters aphotoreceiving portion. As a result, a photoelectric conversion devicecauses the lowering of its sensitivity. Particularly when thephotoelectric conversion device has taken a low F number (the apertureis fully opened), or when a camera or the like has been designed to havea short focal length between a lens and the photoreceiving portion, theproblem becomes remarkable in a peripheral region of in a pixel region.

In recent years, as a method for solving such a problem, Japanese PatentApplication Laid-Open No. 2000-150845 proposes a photoelectricconversion device having a optical wave-guide. FIG. 4 is a typicalsectional view showing one configuration example of a conventionalphotoelectric conversion device. The conventional configuration will benow briefly described with reference to FIG. 4.

In the configuration shown in FIG. 4, an interlayer insulation layer 7having a well structure 21 is formed right above a photoreceivingportion 2. The well structure 21 has a large refraction index layer 8consisting of a material having a large refraction index than theinterlayer insulation layer 7, and reflects incident light 15 which haspassed through the on-chip-microlens 11, on an interface between thelarge refraction index layer 8 and the interlayer insulation film 7.Thus, a conventional photoelectric conversion device increasescondensing efficiency and enhances sensitivity. Here, the conventionalphotoelectric conversion device has an etching-stop layer 12 thereon, inorder not to damage the photoreceiving portion 2 and improve theuniformity of an etching depth when the well structure 21 is formed.

However, the etching-stop layer 12 occasionally causes the reflection ofthe light coming from the upper part on the interface between a largerefraction index layer 8 and itself, due to a difference of therefractive index between them. The reflection on the interface causesreduction and variation in sensitivity. In addition, Japanese PatentApplication Laid-Open No. 2000-150845 proposes a photoelectricconversion device having a patterned etching-stop layer 12 arranged onone part of a photoreceiving portion. In such a configuration, a regionof the photoreceiving portion having the etching-stop layer 12 providedthereon shows reflectance different from that on the region having nofilm thereon, because the regions have different refractive indices; andparticularly, the edge part of the etching-stop layer 12 reflectsincident light thereon to decrease condensing efficiency.

In order to solve the above described problem, the present invention isdirected at providing a photoelectric conversion device which inhibitssensitivity from lowering and varying, and providing a production methodtherefor.

SUMMARY OF THE INVENTION

A photoelectric conversion device according to the present invention forachieving the above described object has a plurality of photoreceivingportions provided in a substrate, an interlayer film overlying thephotoreceiving portions, a large refraction index region which isprovided so as to correspond to the photoreceiving portion and a higherrefractive index than the interlayer film, and a layer which is providedbetween the photoreceiving portion and the large refraction indexregion, and has a lower etching rate than the interlayer film has,wherein the refractive index of the layer of the lower etching rate isbetween the refractive indices of the large refraction index region andthe substrate, and the layer of the lower etching rate is formed so asto cover at least the whole surface of the photoreceiving portion.

The above described configuration can enhance condensing efficiencybecause of having a large refraction index region on a photoreceivingportion, and can reduce the reflection of incident light on the surfaceof the photoreceiving portion because of having the above configuredlayer of a lower etching rate.

Another photoelectric conversion device according to the presentinvention has a plurality of photoreceiving portions provided in thesubstrate, a transfer transistor for transferring the signal charge ofthe photoreceiving portion, an interlayer film overlying thephotoreceiving portions, a large refraction index region which isprovided so as to correspond to the photoreceiving portion, and has ahigher refractive index than the interlayer film, and a layer which isprovided in between the photoreceiving portion and the large refractionindex region, and has a lower etching rate than the interlayer film,wherein the layer of the lower etching rate is arranged so as to coverat least the whole surface of the photoreceiving portion, and cover atleast a part of a gate electrode of the transistor.

Such a configuration can enhance condensing efficiency because of havinga large refraction index region on a photoreceiving portion; can alsoreduce damage to the photoreceiving portion, and the damage to the gateelectrode both occurring in the procedure of producing a photoelectricconversion device, which is preferable for reducing a dark currentflowing in the device, for example.

Another photoelectric conversion device according to the presentinvention has a plurality of photoreceiving portions provided in thesubstrate, an interlayer film overlying the photoreceiving portions, alarge refraction index region which is provided so as to correspond tothe photoreceiving portion and has a higher refractive index than theinterlayer film, a layer which is provided in between the photoreceivingportion and the large refraction index region, and has a lower etchingrate than the interlayer film, and an element isolation region arrangedamong a plurality of the photoreceiving portions, wherein the layer ofthe lower etching rate is arranged so as to cover at least the wholesurface of the photoreceiving portion, and cover at least of a part ofthe element isolation region.

A photoelectric conversion device having such a configuration canincrease condensing efficiency because of having a large refractionindex region on a photoreceiving portion; and can reduce the damage tothe photoreceiving portion and the damage to an element isolation regionoccurring in the procedure of producing the device.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical sectional view showing one configuration example ofa photoelectric conversion device according to a first embodiment of thepresent invention;

FIG. 2A is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2B is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2C is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2D is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2E is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2F is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2G is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2H is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 2I is a view for describing a process of producing a photoelectricconversion device shown in FIG. 1;

FIG. 3 is a typical sectional view showing one configuration example ofa photoelectric conversion device according to a second embodiment ofthe present invention;

FIG. 4 is a typical sectional view showing one configuration example ofa conventional photoelectric conversion device;

FIG. 5A is a view for describing a process of producing a photoelectricconversion device according to a third embodiment of the presentinvention; and

FIG. 5B is a view for describing a process of producing a photoelectricconversion device according to a third embodiment of the presentinvention.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments according to the present invention will be now describedwith reference to the drawings. FIG. 1 is a typical sectional viewshowing one configuration example of a photoelectric conversion t deviceaccording to a first embodiment.

As is shown in FIG. 1, a photoelectric conversion device has a pluralityof photoreceiving portions 102 formed at regions across a predetermineddepth from the surface, in a semiconductor substrate 101; elementisolation regions 103 provided in between the adjacent photoreceivingportions; an etching-stop layer 120 of a layer having a lower etchingrate than an upper layer has, formed on the surface of a semiconductorsubstrate 101 so as to cover the whole surface of the photoreceivingportion 102; a first insulation film 104 provided on the etching-stoplayer 120; and a transistor for transferring an electric charge formedaround the surface of the semiconductor substrate 101, though it is notshown in the drawings. In the above configuration, the etching-stoplayer 120 may be arranged on the upper part of the transistor.

A photoelectric conversion device further has a first pattern 105 and asecond pattern 107 provided so as to overlie a first insulation film104, which are electric wiring for transmitting electric signals from aphotoreceiving portion 102 to the outside. As shown in FIG. 1, the firstpattern 105 is formed on the first insulation film 104. The secondpattern 107 is formed on the second insulation film 106 formed on thefirst pattern 105, so as to lie right on the first pattern 105. Thesecond pattern 107 is covered with a protective layer 108. The firstpattern 105 and the second pattern 107 are provided on the upper part ofa region between the adjacent photoreceiving portions 102 and alsofunctions as a light shielding film for preventing a light to enter eachphotoreceiving portion 102 from entering another photoreceiving portion102. The first insulation film 104 and the second insulation film 106work as an interlayer insulation film for insulating each electricwiring layer from the other.

A photoelectric conversion device further has a well-shaped openingformed in a first insulation film 104, a second insulation film 106 anda protective layer 108 so as to reach the surface of an etching-stoplayer 120 on a photoreceiving portion 102 from the protective layer 108side. The aperture is filled with a large refraction index layer made ofa material having a higher refractive index than the protective layer108 and the interlayer insulation film have. The large refraction indexlayer filled in the well-shaped opening is flattened to form a largerefraction index region 110.

A photoelectric conversion device also has a color filter layer 112provided on a protective layer 108 through the first flattened layer111, and a microlens 114 further provided on the color filter layer 112through the second flattened layer 113.

In a photoelectric conversion device according to the presentembodiment, an etching-stop layer 120 having a refractive index inbetween a large refraction index region 110 and the semiconductorsubstrate 101 covers the whole surface of a photoreceiving portion 102.As a result, the photoelectric conversion device allows the light whichshould have reflected on the end of the etching-stop layer 120 in aconventional photoelectric conversion device that has the etching-stoplayer 120 formed on one part of the surface of the photoreceivingportion, into the photoreceiving portion 102, improves condensingefficiency and inhibits its sensitivity from varying. In other words,such an etching-stop layer 120 having such a refractive index can reducereflectance on those interfaces. Further, it is enabled to take in thelight output to outside of the high refraction index region by exceededtotal reflective angles in the interface of the high refraction indexregion and the interlayer insulation film. Moreover it is enabled toalso take in the light which not have input putting in the highrefraction index region directly. Moreover it is enabled to also take inthe light which is incident in the high refraction index region but inan outside of a total reflection region at an interface between the highrefraction index region and the an interlayer insulating layer. Moreoverit is enabled to also take in the light which is incident indirectly inthe high refraction index region.

A photoelectric conversion device also makes the light (incident light115 shown in FIG. 1) which has entered a large refraction index region110 through the microlens 114 from the outside reflect on the side wallof the large refraction index region and introduces it into aphotoreceiving portion 102, because the large refraction index region110 has a higher refractive index than a protective layer 108 and aninterlayer insulation film have. Thus, the large refraction index region110 in a well-shaped opening plays a role as an optical waveguide, andcan efficiently lead the light condensed by the microlens 114 into thephotoreceiving portion 102. As a result of this, the photoelectricconversion device can attain high sensitivity, even when having a low Fvalue or a short focal distance between the lens and the photoreceivingportion.

In the next place, a method for producing a photoelectric conversiondevice shown in FIG. 1 will be described with reference to FIGS. 2A to2I.

A photoelectric conversion device is produced by the steps of: at first,preparing a semiconductor substrate 101 made of a silicon wafer or thelike, as shown in FIG. 2A; forming an element isolation region 103 inthe inner part around the surface of the semiconductor substrate 101, byusing a STI (shallow trench isolation) technique; subsequently, forminga diffusion layer to become a photoreceiving portion 102 of a photodiode and a diffusion layer of a source electrode and a drain electrodeof the transistor which is not shown in the figures, across a regionreaching the inside of the substrate from the surface of thesemiconductor substrate 101, through forming a photoresist pattern onthe semiconductor substrate 101, and performing ion implantation andheat treatment; and then, forming a gate insulation film and a gateelectrode of the transistor, which are not shown in the figures, in asimilar process to the conventional one. In the above steps, thesemiconductor substrate 101 may have at least of a natural oxide filmand a part of the gate insulating film are formed on the surface, thoughit is not shown in the figures. However, the natural oxide film issufficiently thinner than a wavelength of light, so that the interfacesalmost do not reflect light. Subsequently, an etching-stop layer 120 isformed with a CVD (vapor deposition) method or the like. Here, theetching-stop layer 120 is formed of SiN with a LP (low pressure)-CVDmethod. In the step, the layer of SiN is formed so as to occupy a largerarea at least than the surface of the photoreceiving portion.Subsequently, the first insulation film 104 is formed on theetching-stop layer 120 with the CVD method or the like. Here, it isrecommended to flatten the surface of the first insulation film 104 witha CMP (chemical-mechanical polishing) method, so that patterningprecision can be improved in the subsequent step.

A photoelectric conversion device is subsequently produced by the stepsof: forming a metallic film made of Al, Mo, W, Ta, Ti or Cu or an alloymainly containing them, on the first insulation film 104, with asputtering method, a CVD method, an electrolytic plating method or thelike; after that, forming the first pattern 105 into a desired shape, byremoving the metallic film of a part locating above a photoreceivingportion 102 with a lithography process and an etching process;

then, forming the second insulation film 106 made of SiO or a materialmainly containing it on the first insulation film 104 and the firstpattern 105 with the CVD method; flattening the top surface of thesecond insulation film 106 with the CMP method; next, forming a metallicfilm made of Al, Mo, W, Ta, Ti or Cu or an alloy mainly containing themsimilarly to the first pattern 105, on the second insulation film 106with a sputtering method, a CVD method, an electrolytic plating methodor the like; and forming the second pattern 107 into a desired shape, byremoving a part locating above the photoreceiving portion 102 with thelithography process and the etching process.

A photoelectric conversion device is further subsequently produced bythe steps of: forming a protective layer 108 having an insulation filmsuch as a SiN film, a SiON film and a SiO film on the second pattern 107and the second insulation film 106 with a CVD method, as shown in FIG.2B; and then, forming a photoresist pattern 109 which works as anetching mask for opening a part right above a photoreceiving portion102, on the protective layer 108, as shown in FIG. 2C.

Then, those layers are anisotropically etched toward a photoreceivingportion 102 by using the photoresist pattern 109 as an etching mask, asshown in FIG. 2D. When the etched part reaches an etching-stop layer120, an etching rate decreases. At this time, etching is stopped. Thus,a well-shaped opening 130 is arranged so as to penetrate and themultilayered insulation film consisting of a protective layer 108, thesecond insulation film 106 and the first insulation film 104. In theetching step, each insulation film of the multilayered insulation filmis etched in an optimal etching condition for removing each film. Theetching condition which is adopted at least in a stage when the etchedpart reaches the etching-stop layer 120 needs to have a sufficientlyhigh selective etching ratio of the first insulation film 104 to theetching-stop layer 120 (=the etching rate of the first insulation film104/the etching rate of the etching-stop layer 120). Namely, theetching-stop layer 120 shall have a lower etching rate than the firstinsulation film 104 has.

By the way, an etching-stop layer 120 has only to be formed so as tocover at least the whole surface of a photoreceiving portion, and needsnot to be formed on other parts, unless required. However, it ispreferable to form the etching-stop layer 120 so as to cover at least apart of the gate electrode of a transistor (not shown) for transferringan electric charge, because the etching-stop layer 120 reduces damageonto a gate electrode occurring in a subsequent production step, andconsequently reduces a dark current passing through a photoelectricconversion device. A site which does not need to be covered with theetching-stop layer 120 is, for instance, a contact portion which isopened on the gate electrode in order to connect a gate electrode to theelectric wiring of an upper layer.

It is also preferable to form an etching-stop layer 120 on at least of apart of an element isolation region 103 such as STI, similarly to thecase on the gate electrode, because the etching-stop layer 120 protectsthe STI from being damaged in a production step of forming holes.

Subsequently, as shown in FIG. 2E, a photoresist pattern 109 on aprotective layer 108 is removed by at least one of oxygen plasmatreatment and organic peeling liquid treatment. After that, a largerefraction index layer 117 which becomes a large refraction index region110 afterwards is formed on a well-shaped opening 130, with a FIDP(high-density plasma)-CVD method, as shown in FIG. 2F.

Here, the refractive index of the etching-stop layer 120 is set to asimilar value to that of a large refraction index region 110, or a valuein between the refraction indices of a semiconductor substrate 101 andthe large refraction index region 110. Thereby, the etching-stop layercan reduce the reflection of incident light onto the surface of aphotoreceiving portion.

When an anti-reflection coating for reducing the reflection of theincident light onto the surface of a photoreceiving portion is formed onthe surface of the photoreceiving portion of the semiconductor substrate101, it is preferable to set the refractive index of an etching-stoplayer 120 at around a value in between the refractive indices of theanti-reflection coating and a large refraction index region 110.Alternatively, the refractive index of the etching-stop layer 120 may beset to a value equal to that of the large refraction index region 110 orthe anti-reflection coating.

Here, a specific example on a method for forming a large refractionindex layer 117 will be described. The example is a method, when SiN(refractive index n=1.95) is employed for an etching-stop layer 120, forfilling a recess with an aperture diameter of 2 μm and an aperture depthof 3.5 μm with the same material SiN as is used in the etching-stoplayer 120, with a high-density plasma CVD method.

In general, when a photoreceiving portion 102 is etched with a dryetching process, the process may increase a dark current and a pixeldefect of a photoelectric conversion device, due to the plasma damage.Particularly, when even a region very close to the photoreceivingportion 102 is etched as in the case of the present embodiment, theinfluence of the plasma increases. For this reason, in the first step, aSiN film is formed into the thickness of about 5,000 angstroms, in adamage-relaxing film-forming condition 1 which has reduced a RF bias to0 to 400 W and controlled other conditions to the followings: [gas massflow: Ar: 200 sccm, N2: 135 sccm, SiH4: 19 sccm, pressure: 8 mTorr, RFpower: 3,000 W, RF bias power: 300 W and film-forming time: 5 min].

Subsequently, the SiN film is formed into the thickness of about 2 μm inthe following film-forming condition 2 to fill a well-shaped opening:[gas mass flow: Ar: 126 sccm, N2: 360 sccm, SiH4: 84 sccm, pressure: 8mTorr, RF power: 3,000 W, RF bias power: 3,500 W and film-forming time:5 min].

Furthermore, the SiN film is formed into the thickness of about 1 μm inthe following film-forming condition 3 to promote the flattening of thetop part of the opening: [gas mass flow: Ar: 126 sccm, N2: 360 sccm,SiH4: 84 sccm, pressure: 8 mTorr, RF power: 3,000 W, RF bias power:5,000 W and film-forming time: 2.5 min]. In the above condition, the RFbias power is increased to 5,000 W, by which a salient part isrelatively more etched than a recess part is, and a part right above aphotoreceiving portion is relatively flattened. As a result, in asubsequent step for flattening the surface of a SiN film, an amount ofthe SiN film to be removed by etching or to be polished by CMP treatmentis decreased, or the step itself is eliminated, any of which is anadvantage. By employing such a high-density plasma CVD method, awell-shaped opening with a high aspect ratio (=opening depth/openingdiameter) can be filled with a film. In addition, by changing the RFbias power to be applied on a substrate, the damage to be given to thephotoreceiving portion 102 can be reduced, and the top surface of theformed film can be flattened.

In the above embodiment, a SiN film is used for an etching-stop layer120 and in a large refraction index region 110, but any material can beused as long as it has a higher refractive index than the firstinsulation film 104 and the second insulation film 106 have, andprovides desired condensing efficiency. As described above, it ispreferable that the etching-stop layer 120 has the refractive indexsimilar to that of the large refraction index region 110 or in betweenthe refractive indices of a semiconductor substrate 101 and the largerefraction index region 110. Accordingly, the material for theetching-stop layer 120 is not limited to the SiN film, but may employ,for instance, a SION film (of which the refractive index can be adjustedto 1.45 to 2.0).

In addition, the same material can acquire a different refractive indexby changing a production method. For instance, when using a SiN film foran etching stop layer 120 and a large refraction index layer 117, theetching-stop layer may be the SiN film formed with a low pressure CVDmethod, and the large refraction index layer 117 may be with a HDP-CVDmethod. In the above step, the SiN film formed with the HDP-CVO methodtends to have lower density and a lower refractive index than those withthe low pressure CVD method. Thus, by changing a production method, eventhe same material can acquire a desired refractive index.

In the above embodiment, the film-forming condition for filling awell-shaped opening with SiN consisted of mainly three differentconditions, but the film-forming condition may be an appropriatelyselected single condition or combination of a plurality of conditions,as long as the condition imparts a large refraction index region made ofthe SiN desired condensing efficiency and basic performance as a sensor.

Subsequently, the surface of a large refraction index layer 117 ispolished with a CMP method to be flattened, and a large refraction indexregion 110 is formed as shown in FIG. 2G. Here, the CMP method wasemployed for flattening the surface, but an etching back method with theuse of a plasma etching technique may be employed. In addition, thelarge refraction index layer 117 was polished to be flattened till thesurface reaches the top face of a protective layer 108, but thepolishing may be stopped when the surface is still in the largerefraction index layer 117. In the above step, if the same function asin the protective layer 108 was given to the large refraction indexlayer 117, the step of forming the protective layer 108 described inFIG. 2B can be omitted.

After that, the first flattened layer 111 is formed with an applicationmethod as shown in FIG. 2H. Subsequently, a base material for a colorfilter layer 112 is applied on the first flattened layer 111, and thenby light-exposing and developing the layer, a color filter layer 112(Red layer, Green layer and Blue layer in case of primary color) isformed.

Furthermore, as shown in FIG. 2I, the second flattened layer 113 isformed on the color filter layer 112 with an application method, andsubsequently, the base material for a microlens 114 is applied on thesecond flattened layer 113. Then, the microlens 114 is formed bylight-exposing and developing the material to form a predeterminedpattern, and reflowing the formed pattern. By the above described steps,a photoelectric conversion device is produced.

In the method for producing a photoelectric conversion device accordingto the present embodiment, an etching-stop layer 120 is formed so as tocover at least the whole surface of a photoreceiving portion. As aresult, when a well-shaped opening is formed for a large refractionindex region 110, the opening can be not only formed closer to an areaof the surface of the photoreceiving portion, but also can be preventedfrom penetrating into the surface of the photoreceiving portion.

The etching-stop layer 120 which covers the surface of eachphotoreceiving portion 102 has also preferably a wider area than that ofan interface between a large refraction index region 110 and theetching-stop layer 120. Then, the etching-stop layer prevents a lightrefracted in the large refraction index region 110 from shining theoutside of the photoreceiving portion 102, and consequently improvescondensing efficiency.

In addition, in the above described embodiment, an element isolationregion 103 was formed with a STI method, but it may be formed with aLOCOS method (a method of locally oxidizing silicon). In any elementisolation region, as shown in each of FIGS. 1 to 2A through 2I, anetching-stop layer 120 may be arranged in the upper part. It isnecessary to cover the part at least, although the whole may be covered.

In the next place, as a second embodiment, a photoelectric conversiondevice with no etching-stop layer 120 provided thereon will bedescribed.

FIG. 3 is a typical sectional view showing one configuration example ofa photoelectric conversion device according to a second embodiment. InFIG. 3, the same reference numeral as in FIG. 1 is attached for the samecomponent as in the photoelectric conversion device shown FIG. 1, and adetailed description for the component is omitted. In addition, anelement isolation region and a transistor for transferring an electriccharge are not shown in the figure because of being the same as in aprevious case.

A photoelectric conversion device shown in FIG. 3 has the firstinsulation film 125 formed on a semiconductor substrate 101 having aphotoreceiving portion 102 formed therein; and sets the refractive indexof the first insulation film 125 equal to that of a large refractionindex region 110. In this case as well, the refractive index of thefirst insulation film 125 may be set to a value in between therefractive indices of the semiconductor substrate 101 and the largerefraction index region 110.

A method for producing a photoelectric conversion device shown in FIG. 3will be now briefly described.

The device is produced by the steps of: forming a photoreceiving portion102 and a transistor (not shown) on a semiconductor substrate 101; then,forming the first insulation film 125 thereon, as was shown in FIG. 2A;subsequently, forming the first pattern 105, the second insulation film106 and second pattern 107; after that, forming a protective layer 108and a photoresist pattern 109 thereon with the same treatment method asin the case of FIGS. 2B and 2C; and then, forming a well-shaped openingin the protective layer 108 and the second insulation film 106, throughetching the films in an etching period of time, which is controlled tobe a quotient obtained by dividing the total film thickness of theprotective layer 108 and the second insulation film 106 by an etchingrate. In the etching process, even when an etching amount varies, thefirst insulation film 125 can prevent the opening from reaching thephotoreceiving portion 102. After that, the above substrate is treatedin a similar way to that in the case of FIG. 2E and the remainder, and aphotoelectric conversion device shown in FIG. 3 is produced.

A photoelectric conversion device according to the second embodiment notonly inhibits the lowering of the sensitivity and the variation of thesensitivity among picture elements but also can be etched in a freeretching condition in the etching step, because the first insulation film125 and the second insulation film 106 are not necessarily etched in asecured selective etching ratio.

Now, as a third embodiment, a photoelectric conversion device having anetching-stop layer 120 arranged so as to cover one part of the gateelectrode of a transistor for transferring an electric charge will bebriefly described with reference to FIGS. 5A and 5B.

Both FIGS. 5A and 5B are typical sectional views showing oneconfiguration example of a photoelectric conversion device, and showingthe production steps therefor. In FIGS. 5A and 5B, the same referencenumeral as in FIG. 1 is attached for the same component as in thephotoelectric conversion device shown FIG. 1, and detailed descriptionfor the component is omitted.

In FIG. 5A, a gate electrode 140 of a transistor for transferring anelectric charge is arranged in the vicinity of the surface of thesemiconductor substrate 101, and of the diffusion region 150 of thetransistor formed in the substrate. In addition, a contact portion 145for electrical conduction is formed on the gate electrode 141 of anothertransistor. Here, each gate electrode has a side wall 143.

In addition, an etching-stop layer 120 is arranged on a photoreceivingportion 102, so as to cover a wider area than that of the photoreceivingportion 102, and further is arranged so as to cover one part of the gateelectrode 140 of the transistor for transferring an electric charge, inthe present embodiment. Here, the previously described side wall 143 andthe etching-stop layer 120 are formed through etching the same layer.Those two components can be easily formed because of being formed fromthe same layer.

FIG. 5B is a typical sectional view of a photoelectric conversion deviceaccording to the present embodiment, which has been produced bypatterning a resist mask 135 on a protective layer 108 in FIG. 5A, andetching the above layers for preparing a well-shaped opening 130.Afterwards, the well-shaped opening is filled with a material having ahigher refractive index than the first insulation layer 104 and thesecond insulation layers 106 have and capable of providing desiredcondensing efficiency; then the surface is flattened; and thus, a largerefraction index region 110 is formed.

In the above configuration where an etching-stop layer 120 is formed soas to cover one part of the gate electrode 140 for transferring anelectric charge, the etching-stop layer 120 reduces damage to the gateelectrode 140 given in a subsequent step. The step of giving the damageto the gate electrode 140 includes the step of HDP-CVD for filling awell-shaped opening 130 with the large refraction index material, andthe step of ion-implantation when forming a diffusion region in theperiphery. The above configuration reduces the damage due to thosesteps, and as a result, can reduce a dark current of the photoelectricconversion device.

As described above, an etching-stop layer 120 has only to cover one partof a gate electrode 140 for transferring an electric charge, andaccordingly may cover the whole surface thereof. If necessary, a part ofa contact portion 145, for instance, may be removed.

The etching-stop layer 120 may cover further at least of a part of anelement isolation region. Then, it can inhibit the element isolationregion from being damaged in production steps.

In addition, the refractive index of an etching-stop layer 120 accordingto the present embodiment may be adjusted to the same value as in alarge refraction index region 110, or a value in between the refractiveindices of a semiconductor substrate 101 and the large refraction indexregion 110, though it is not specified in the present embodiment. Whenhaving such a refractive index, the etching-stop layer 120 can furtherinhibit reflection at the interfaces thereof from occurring on aphotoreceiving portion.

Up to this point, the present invention has been described in detail.However, the present invention is not limited to the above describedembodiment, but an appropriate combination of a refractive index of anetching stop layer with the arrangement thereof and the like can beemployed.

This application claims priority from Japanese Patent Application No.2004-355364 filed Dec. 8, 2004, which is hereby incorporated byreference herein.

1. A photoelectric conversion device having a plurality ofphotoreceiving portions provided in a substrate, an interlayer filmoverlying the photoreceiving portions, a large refraction index regioncorresponding to the photoreceiving portion and has a higher refractiveindex than the interlayer film, and a layer which is provided betweenthe photoreceiving portion and the large refraction index region, andhas a lower etching rate than the interlayer film: wherein therefractive index of the layer of the lower etching rate is between therefractive indices of the large refraction index region and thesubstrate, and the layer of the lower etching rate is formed so as tocover at least the whole surface of the photoreceiving portion.
 2. Thephotoelectric conversion device according to claim 1, wherein the layerof a lower etching rate and the large refraction index region are asilicon nitride film or an silicon oxynitride film.
 3. The photoelectricconversion device according to claim 1, wherein the layer of a loweretching rate on each photoreceiving portion is formed so as to cover awider area than the large refraction index region has.
 4. Thephotoelectric conversion device according to claim 1, wherein a contactportion for connection is arranged therein and a layer of a loweretching rate is not arranged around the contact portion.
 5. Thephotoelectric conversion device according to claim 1, wherein the largerefraction index region having a higher refractive index than theinterlayer film has is formed by plasma CVD.
 6. The photoelectricconversion device according to claim 1, wherein the large refractionindex region having a higher refractive index than the interlayer filmhas is formed by filling the region with a large refraction indexmaterial and then flattening the surface.
 7. A photoelectric conversiondevice having a plurality of photoreceiving portions provided in thesubstrate, a transfer transistor for transferring a signal charge of thephotoreceiving portion, an interlayer film overlying the photoreceivingportions, a large refraction index region which is provided so as tocorrespond to the photoreceiving portion and has a higher refractiveindex than the interlayer film, and a layer which is provided in betweenthe photoreceiving portion and the large refraction index region, andhas a lower etching rate than the interlayer film: wherein the layer ofthe lower etching rate is arranged so as to cover at least the wholesurface of the photoreceiving portion, and cover at least of a part of agate electrode of the transistor.
 8. The photoelectric conversion deviceaccording to claim 7, wherein the refractive index of the layer of alower etching rate is between the refractive indices of the largerefraction index region and the substrate.
 9. The photoelectricconversion device according to claim 7, wherein the layer of a loweretching rate and the large refraction index region are independently asilicon nitride film or an silicon oxynitride film.
 10. Thephotoelectric conversion device according to claim 7, wherein the layerof a lower etching rate on each photoreceiving portion is formed so asto cover a wider area than the large refraction index region has. 11.The photoelectric conversion device according to claim 7, wherein acontact portion for connection is arranged therein and a layer of alower etching rate is not arranged around the contact portion.
 12. Thephotoelectric conversion device according to claim 7, wherein the largerefraction index region having a higher refractive index than theinterlayer film has is formed by plasma CVD.
 13. The photoelectricconversion device according to claim 7, wherein the large refractionindex region having a higher refractive index than the interlayer filmhas is formed by filling the region with a large refraction indexmaterial and then flattening the surface.
 14. A photoelectric conversiondevice having a plurality of photoreceiving portions provided in thesubstrate, an interlayer film overlying the photoreceiving portions, alarge refraction index region which is provided so as to correspond tothe photoreceiving portion and has a higher refractive index than theinterlayer film, a layer which is provided in between the photoreceivingportion and the large refraction index region, and has a lower etchingrate than the interlayer film, and an element isolation region arrangedbetween a plurality of the photoreceiving portions: wherein the layer ofthe lower etching rate is arranged so as to cover at least the wholesurface of the photoreceiving portion, and cover at least of a part ofthe element isolation region.
 15. The photoelectric conversion deviceaccording to claim 14, wherein a transfer transistor for transferring asignal charge of the photoreceiving portion is arranged therein, and alayer of a lower etching rate is arranged on the whole surface of thesubstrate so as to cover the gate electrode of the transistor.